A commercially available standard Schottky electron source, Zr/O/W(100), uses the natural tendency of the tungsten (W) substrate material to re-form during processing to create a flat facet composed of the (100) crystallographic plane. During operation, a specific combination of temperature and electric field allows diffusion of zirconium (Zr) and oxygen (O) to create a low work function on the (100) facet plane at the apex of the emitter tip. This (100) facet or flat is responsible for the low work function in the presence of Zr and O and shapes the electric field at the apex. The work function of currently available commercial sources of Zr/O/W(100) electron emitters is dependent on temperature, electric field, and vacuum levels. Because of this dependence, Zr/O/W(100) electron sources are limited in the amount of current they can emit. Such limitation can be defined as total beam current, angular intensity, brightness, or reduced brightness. Currently available Zr/O/W(100) electron sources are typically limited to angular intensities of 0.2 to 1.0 mA/sr (milliamps/steradian).